ABSTRACT Unstable/vulnerable plaques, that are characterized by a thin cap fibroatheroma, necrotic core due to lipid pools by macrophages, may result in serious clinical conditions, including transient ischemic attack, stroke, aphasia, and other motor defects. Inflammation, apoptosis of plaque vascular smooth muscle cells (VSMCs) and increased degradation of extracellular matrices are the primary underlying cause of plaque instability. Despite extensive research, the causative factor(s) in the initiation of vulnerable plaque is unknown. Based on our novel findings, we hypothesize that lipopolysaccharide (LPS) or minimally oxLDL induce vulnerable/unstable carotid plaque and antagonizing TREM-1 and TLR4 stabilizes atherosclerotic plaque in carotid arteries. These studies will be performed in atherosclerotic Yucatan microswine model with occlusion of carotid arteries that resemble to occlusive carotid artery disease in human. This model will mimic the real situation in patients with carotid artery disease, and thus, will make a direct contribution to understanding the pathophysiology of the disease process and allow us to develop better therapeutic approaches to stabilize vulnerable plaques. Aim 1: The hypothesis predicts that the administration of LPS or minimally oxLDL in the carotid artery of atherosclerotic Yucatan microswine induces histological, morphological and biochemical features of carotid plaque like human unstable plaque by increasing the expression of TREM-1, MMP-1, MMP-9, TLR4 and M1 macrophages and decreasing collagen, TREM-2, and M2 macrophages. We will probe the effect of LPS-induced plaque instability by gray scale and Doppler ultrasound, Optical coherence tomography and the histology, immunohistochemistry and immunofluorescence to analyze thinned fibrous cap, inflammation, necrotic core, intimal proliferation with foamy macrophages, VSMCs apoptosis, lipid core, necrosis, intraplaque hemorrhage, and vascular remodeling. These findings will be compared in-vivo and in-vitro in the stable and unstable carotid plaques. We will also examine and compare the mRNA transcripts and protein expression of TREM-1, TREM-2, MMP-1, MMP-9, collagen I(?1), collagen III(?1), M1-M2 macrophages, VSMCs, expression and interaction of TLRs with TREM-1, in addition to the effect of TREM-1 on foam cell formation, release of inflammatory cytokines, and in the cross-talk between VSMCs and macrophages. Aim 2: The hypothesis predicts that the administration of TREM-1 and TLR4 antagonists will prevent the development of unstable plaque in the carotid artery of atherosclerotic swine. Effect of an inhibitory TREM-1 peptide, LR12, a scrambled peptide (placebo), and TAK-242, a TLR4 antagonist, will be examined in carotid arteries following LPS/oxLDL administration. Also, in-vivo and in-vitro functional/biochemical parameters will be examined. The findings from this study will confirm if TREM-1 is a novel target for therapeutic intervention and extend the knowledge to develop better molecules to antagonize TREM-1 and design phase I clinical trials.